The present invention relates to hydraulic tappets and in particular hydraulic tappets for overhead cam shaft internal combustion engines.
In conventional overhead cam shaft internal combustion engines, a cup shaped tappet is located over the end of the valve stem with an adjusting shim interposed therebetween. The tappet is slidingly located in a bore in the cylinder head, so that the flat face thereof is engaged by a cam. In order to ensure that the valve will close fully in spite of thermal expansion of the components, it is necessary to maintain a clearance between the face of the tappet and the base circle diameter of the cam. The thickness of the adjusting shim is selected to provide a set clearance between the face of the tappet and the base circle diameter of the cam, so that a clearance will be maintained therebetween, over the operating temperature range of the engine, while noise created thereby is minimized.
The present invention provides a hydraulic tappet in which the inter-engaging surfaces of the cam and tappet are maintained in engagement, a clearance being provided between the tappet and valve stem, the load applied to the tappet being transmitted to the valve stem by means of hydraulic fluid.